1. Field of the Invention
The present invention relates to a method for controlling the recording speed of a multi-layered optical disc. In particular, this invention provides a method for deciding the recording speed of each recording layer of a multi-layered optical disc when an optical drive records the information on the disc.
2. Description of the Related Art
The quality of an optical disc influences the reliability of data recorded on the disc. In the manufacturing process of a recordable disc, the physical signal of the disc (such as the wobble signal, the tracking error or the focus error etc.) is not good if the dye on the disc is coated disproportionately or if the disc is warped. This reduces the quality of data recording when data is recorded using a high recording speed on some zones of the disc. This issue usually occurs at the outside area of the disc. Furthermore, in order to store more data, the different kinds of recordable discs can be either monolayered, double-layered to multi-layered. If the number of layers of the recordable disc is higher, the difficulty of manufacturing increases and quality control is harder. As such, there is a large disparity between the quality of discs available on the market. So it's easy to see why guaranteeing data recording quality on a disc is an important issue for an optical drive with a recording function. In the prior art this problem has been dealt with by reducing the recording speed to enhance recording quality.
FIGS. 1A and 1B show a schematic diagram of a double-layered disc of the prior art. FIG. 1A shows a double-layered disc 10 having a first recording layer 12 and a second recording layer 14. The first recording layer 12 and the second recording layer 14 are on a parallel track path (PTP). The recording sequence of the double-layered disc 10 moves from the inner location 121 to the outer location 122 of the first recording layer 12, then from the inner location 141 to the outer location 142 of the second recording layer 14. The arrows in FIG. 1A show the recording direction of the recording layers.
FIG. 1B shows another double-layered disc 16 having a first recording layer 18 and a second recording layer 20. The first recording layer 18 and the second recording layer 20 are on opposite track path (OTP). The recording sequence of the double-layered disc 16 is from the inner location 181 to the outer location 182 of the first recording layer 16, then from the outer location 201 to the inner location 202 of the second recording layer 20. The arrows in FIG. 1B show the recording direction of the recording layers.
FIG. 2 shows a schematic diagram of the relationship between the recording speed and the location of a double-layered disc on opposite track path of the prior art. The first recording layer of the disc is divided into four zones, Z1, Z2, Z3 and Z4. Each zone individually corresponds to one recording speed, such as 2 times speed, 4 times speed, 6 times speed and 8 times speed (2×, 4×, 6× and 8×). Moreover, the second recording layer of the disc is also divided into four zones, Z5, Z6, Z7 and Z8. Each zone also individually corresponds to one recording speed, such as 2 times speed, 4 times speed, 6 times speed and 8 times speed (2×, 4×, 6× and 8×). When an optical drive is recording data on a disc, the optical drive firstly sets the recording speed according to the location of the zones and the corresponding speed. Secondly, when the optical drive records data on the disc from the inner area to the outer area of the first recording layer, the recording speed goes from low speed to high speed. Then, when the optical drive records data on the disc from the outer area to the inner area of the second recording layer; the recording speed goes from high speed to low speed.
When the quality of a zone of the optical disc is inferior, the optical drive reduces the recording speed at the inferior zone of the optical disc in order to guarantee the reliability of the recorded data, as shown in FIG. 3. When the quality of the optical disc is inferior, such as in zone Z3 of the first recording layer of the optical disc, the optical drive reduces the recording speed from 6× to 4× and records data on the rest of the first recording layer and the second recording layer at this speed, 4×. Although this method improves the recording quality, it still uses a low recording speed to record data on the zone of the second recording layer even though it is suitable for using a high recording speed. The recording time is therefore longer and the efficiency becomes lower. As such the method does not ensure both quality and efficiency.